1. Field of the Invention
The present invention generally relates to semiconductor devices, and particularly relates to a semiconductor device provided with test functions.
2. Description of the Related Art
The SiP (system in package) structure has a configuration in which a plurality of LSI (large scale integrated circuit) chips are provided and connected together inside a single package. FIGS. 1A and 1B are drawings showing an example of the SiP configuration. FIG. 1A illustrates a side view of an SiP, and FIG. 1B shows a plan view of the SiP. The SiP has a structure in which a first chip 10 and a second chip 11 are sealed inside a package 12. This structure provides a highly functional, small-sized semiconductor device.
In the SiP shown in FIG. 1B, the first chip 10 and the second chip 11 have internally-confined terminals 13 and external-connection terminals 14. The internally-confined terminals 13 serve to connect between the first chip 10 and the second chip 11, and are sealed inside the package 12 so that no access from the exterior can be made. The external-connection terminals 14 are connected to the exterior of the package 12 so as to allow access to be made to the first chip 10 and the second chip 11 from the exterior of the package 12.
Generally, tests conducted at the time of shipment of LSIs need to make sure that no leak defect is present between LSI terminals. This is done by applying a voltage between adjacent terminals-subjected to inspection and by measuring a current flowing between these terminals so as to check whether a leak current is present between the terminals, i.e., whether there is a leak defect.
In the case of the SiP as illustrated in FIG. 1, no access can be made from the exterior of the package to the terminals (internally-confined terminals 13) that provide couplings between the chips inside the package and for which there is no need to exchange signals with the exterior. There is thus a problem that the measurement of leak currents between these terminals cannot be made. In order to conduct a leak defect test with respect to these terminals, either these terminals for which there is no need for external connection should be connected to the exterior or there is a need for a method of measuring inter-terminal leak currents without accessing these terminals from the exterior.
As a method of detecting a leak current without accessing terminals from an exterior, it is conceivable to set the outputs of the terminals equal to HIGH and LOW alternately and to monitor the power supply current consumed by the LSI core. FIG. 2 is a drawing for explaining a method of detecting a leak defect of internally-confined terminals. In FIG. 2, the first chip 10 and the second chip 11 include core circuits 20 and 21, respectively. The core circuits 20 and 21 are coupled to each other via the internally-confined terminals 13, and the core circuit 20 transmits signals to the core circuit 21 via output buffers 22.
In FIG. 2, two adjacent terminals are connected to each other through an inter-terminal short-circuit defect A. With one of these terminals set to HIGH and the other set to LOW, a leak current i2 flows through the inter-terminal short-circuit defect A. A power supply voltage VDD supplied from the exterior of the package 12 to a power supply terminal 23 is monitored to detect an increase caused by the leak current i2, thereby detecting a short-circuit between terminals.
Patent Document 1 discloses providing a means to supply power separately to all the bear chips on a multi-chip circuit board, and teaches a test procedure by which power is supplied only to a bear chip to be tested among the plurality of bear chips while no power is supplied to the remaining bear chips.
[Patent Document 1] Japanese Patent Application Publication No. 2000-111617
In the method of detecting a leak current by monitoring a power supply current as shown in FIG. 2, a current i1 consumed in the core circuit and the leak current i2 are combined together when they are measured. In general, most leak defects are not a complete short-circuit between terminals, but are rather a high-resistance connection between terminals. In such a case, the leak current i2 has a small current amount compared with the current i1 consumed by the core circuit. When current consumption increases due to a leak during the monitoring of consolidated current consumption, therefore, it is difficult to decide whether the increase in the current consumption is caused by a leak or caused by fluctuation of currents consumed by the core circuit.
Accordingly, there is a need for a semiconductor device which can detect an inter-terminal leak defect reliably without accessing terminals.